const Fn = (arr) => {
  return arr.map(item => item + 1)
}

Fn([5,6,7]);

let obj = Object.assign({},{y: 9999});

let prx = new Proxy(obj,{
  set(key,val) {
    obj[key] = val
  },
  get(key) {
    return obj[key]
  }
});

console.log(prx);

const fn = (arr) => arr.map(item => item + 1)

fn([1,2,3])